Electronic timer



United States Patent 1,746,525 2/1930 Darrah 2,295,366 9/1942 Stout.... 3,419,034 12/1968 Hart lnventor Appl. No.

Filed Patented Assignee ELECTRONIC TIMER 9 Claims, 1 Drawing Fig.

[1.8. CI. .l

Int. Cl

References Cited UNITED STATES PATENTS G05d 11/00 Field of Search Primary Examiner-Alan Cohan Attorney-Hill, Shennan, Meroni, Gross & Simpson ABSTRACT: A photo copy toner density control device having means for sensing the concentrate density of a photo copier fluid and for developing an electrical signal indicative of the sensed concentrate thereof. The output of the sensing means is coupled to a series of transistors so arranged as to have a substantially higher turn on" level than the turn off" level thereof. A capacitive charging device is coupled to the input of the switching transistors, and a given voltage level which turns on the three transistors substantially simultaneously also causes the discharge of the capacitive means, the discharge of which determines the on time of an injection means for adding concentrate to the fluid being sensed. The capacitive means also provides a delay to prevent the too rapid cycling of the timer and thereby avoid the adding of excessive concentrate to the fluid prior to the adequate mixing of the concentrate in the fluid and the associated sensing of the so mixed concentrate by the sensing means.

PATENTED 0&11221970 INVEN'IOR. GEORGE H FATHAUER ELECTRONIC TIMER BACKGROUND OF THE INVENTION Field of the Invention The field of art to which this invention pertains is an elec tronic timer, and, in particular, an electronic timer for determining the injection time of concentrate fluid in a photo copy device and for preventing the rapid recycling of the injection means to avoid excessive adding of toner concentrate to the photo copier solution.

SUMMARY It is an important feature of the present invention to provide an improved electronic timing device. I

It is also a feature of the present invention to provide a timing device particularly suited for maintaining the required toner concentration of a photo copier solution,

It is an important object of the present invention to provide an electronic timer having simplified means for determining the on time of an output signal.

It is also an object of the present invention to provide an electronic timer having means for preventing the too rapid recycling of the timer, and, accordingly, to' provide an inherent time delay in the turning on',-of the timing switching means.

It is another object of the present invention to provide an electronic timing device for a photo copy concentrate solution actuator which includes means for sensing the concentrate density of the solution and means for injecting specified quantities of added concentrate into the solution and for reevaluating the new concentrate level of the solution prior to the subsequent injection of concentrate toner thereinto.

It is an additional object of this invention to provide an electronic timer having three electronic switching devices wherein the second and third device are turned "on by the turning on" of the first device, and wherein the second device prevents the turning on of the first device until a given input level to the first device is attained, and wherein the turning on of the third device reduces the holding off influence of the second device on the first device thereby allowing the first device to be turned off at a lower voltage level than the turn on level thereof.

It is another object of this invention to provide an electronic timer of the type described above wherein a light beam is passed through a sample of a photo copier solution to be sensed, and a photo sensitive resistor is positioned to receive the light beam after having passed through said sample, and wherein the current level through said resistor provides the input triggering means for the electronic timer switching devices.

It is also an object of this invention to provide an electronic timer of the type described above wherein a capacitor is coupled to the input of a first switching device of the timer, and wherein the subsequent turning on" of the switching devices within the timer causes a discharge ,of the capacitor, and wherein the discharge of the capacitor determines the turn on" time of those switching devices. 7

These and other objects, features and advantages of the present invention will be understood in greater detail from the following description and the associated drawings wherein reference numerals are utilized in designating an illustrative embodiment.

DESCRIPTION OF THE DRAWINGS The drawing to the present invention is a schematic of a power supply, a photo sensing means and an electronic timing DESCRIPTION OF THE PREFERRED EMBODIMENT The electronic timing circuit as shown on the drawing consists essentially of three transistors which are turned on" substantially simultaneously in response to the charging of an input capacitor. The voltage level affecting the charging of the input capacitor is determined by the strength of a light beam passing through a sample of a photo copier fluid. Once a given voltage level is reached, the first transistor is turned on" and the subsequent transistors are also immediately turned on." However, the turning on of the third transistor couples a feedback signal to the second transistor for reducing the biasing level of that transistor and, accordingly, reducing the input voltage level required to turn off the first transistor. Accordingly, a differential is obtained between the turn on" and turn off voltages, which allows the discharge of the capacitor to occur through a period of time which corresponds to the time interval of conduction of the three transistors. Accordingly, a relay for adding toner concentrate to the photo copier fluid solution is held on for a period of time determined by the discharge of the capacitor between the turn on" voltage and the turn off voltage thereof. Also, the presence of the capacitor at the input of the switching devices or transistors prevents the too rapid recycling of the timer and thereby prevents the adding of excess toner concentrate to the photo copier fluid solution.

More specifically, the electronic timer is supplied by means of a standard power supply utilizing a transformer 10 having a primary l1 and a secondary winding 12. The primary 11 is supplied at a pair of terminals 13 and 14 by a standard ll5 volt 60 cycle signal.

The secondary winding 12 has a center tap 15 coupled to ground at 16 and has a pair of rectifiers l7 and 18 for providing full wave rectification. A capacitor 19 is coupled to the output of the rectifiers l7 and 18 for smoothing the resulting signal and together with a resistor 20 and a zener diode 21 and a further resistor 22, provide a substantially uniform DC signal having a constant amplitude for supplying the electronic timer as indicated by the various plus connections shown in the drawing. For instance, the voltage at the terminal 23 may be 9 volts DC and may be coupled to each of the terminals in the drawing indicated by a plus designation.

A sample of photo copier fluid such as a sample 24 may be contained in a translucent container 25 such that a light source 26 will pass a beam through the solution and such that the intensity of the beam after having passed through the solution may be monitored at a photo sensitive resistor 27. The light source 26 is also energized from the standard power supply, and in this case, is directly energized through a line 28 which is coupled directly to the resistor 22.

The photo sensitive resistor 27 together with a set of resistors 29, 30 and 31 may be said to bean indicator means for developing an electrical signal which isrelated to the toner concentration of the fluid sample 24. The resistor 30 is a variable resistor having a pointer 32 for adjusting the resistance thereof and is used to vary the sensitivity of the photo resistor 27. A diode 33 is connected between a junction point 34 and a further junction point 35 and limits the input signal which may be applied to the electronic timing device.

The timing device consists generally of first, second and third devices or transistors 36, 37 and 38.

A capacitance means or capacitor 39 is coupled between the junction point 34 and ground at a point 40 and is also coupled to a base terminal 41 of the transistor 36. When the capacitor 39 attains a given voltage level due to the charging thereof through the resistor 31 by means of the positive source indicated at the junction point 42, the transistor 36 is placed in a conducting state. The turning on of the transistor 36 causes the conduction of a current from the collector terminal 43 to the emitter terminal 44 thereof Such conduction then is coupled directly by means of a line 45 to an emitter 46 of the transistor 37, thereby turning on that transistor.

The turning on" of the transistor 37 then couples a positive signal from the collector 47 thereof through a resistor 48 and a bias resistor 49 to the base 50. of the transistor 38. In this way, the turning onof the transistor 36 controls the turning on of the transistors 37 and 38.

Once the transistor 38 is turned on, current will conduct from a positive terminal at the junction point 51 through a relay coil 52 to the collector terminal 53 and hence to the emitter terminal 54 which is coupled to ground as at 55. The relay coil 52.is shunted by a diode 56 to prevent the collapse of the coil field from developing high voltages across the transistor 53.

The energizing of the coil 52 operates a relay switch 57a which is illustrated schematically. The closing of the switch 57a connects a voltage source at the junction point 58a to a solenoid operated valve 59a or the like and allowsttoner concentrate to flow from a reservoir 600 through a line 61 to the photo copier solution 24.

The relay 52 will, of course, remain on until means are provided for turning off the switching devices 36, 37 and 38? It" is desirable that the switching; devices 36, 37 and 38 remain on for a predetermined period of time, and after having been turned on," it is desirable that they remain ofF until such time as the toner concentrate which has been added to the photo copier solution be allowed to mingle with the solution to assure thatthe reading provided by the photo sensitive resistor 27 is indicative of the measure of toner concentrate in the entire photo copier solution.

The combination of the transistors 36, 37 and 38 provides the necessary circuitry to assure that the relay 52 is turned on and held on for the predetermined period of time. In particular, the transistors 36 and 37 work together in such a way that both transistors must be placed in a conducting state before either transistor can conduct. in particular, the transistor 37 holds the transistor 36 in an condition until the turning on of the transistor 36 would result in sufficient current to turn on the transistor 37;

However, after the turning on" of the transistor 37, the transistor 38 also turns on resulting in a sudden drop in voltage at the line 57 which is coupled directly to the base 58 of the transistor 37. Accordingly, thebias conditions for the transistor 37 are suddenly reduced by the turning on of the transistor 38. Hence, the turn off point for the transistor 36 will be substantially lower than the turn on point due to the change in bias conditions.

For instance, if a charge of 7 volts at the capacitor 39 causes the transistor 36 to conduct, the sudden lowering of the bias at the base 58 of the transistor 37 will cause the three transistors to remain in a conducting state until the voltage at the capacitor 39 is reduced to 2 volts, for instance. This allows the relay 52 to remain in an on" condition until the capacitor has been reduced to the two volt level.

The time which the relay will remain on depends upon the discharge circuit of the capacitor 39. In particular, a resistor 59 is connected in series with the capacitor 39 with respect to further diode 60 and the transistor 38. When the transistor 38 turns on, the capacitor 39 is allowed to discharge through the resistor 59, the diode 60 and the transistor 38. In this way, the on" time of the relay 52 is determined by the value of the resistor 59in combination with the capacitance of the capacitor 39. It is noted that the initial bias conditions for the transistor 37 are provided by a series of resistors 61, 62 and 63 together with a capacitor 64 which is coupled in parallel with the resistor 62.

In addition to determining the on time of the relay 52, the capacitor 39 provides a delay before the recycling of the electronic timer can be accomplished. In particular, after the capacitor 39 has been reduced to two loads, for instance, the capacitor must recharge to the 7 volt level before the switching devices can be retriggered and before additional concentrate can be added to the photo copier solution 24. This allows sufficient time to lapse between injections of fluid into-the solution 24 to assure a proper mixing of the fluid and hence a proper sensing of the fluid concentrate level by means of the photo sensitive resistor 27.

It will be apparent that various modifications and combinations of the features of my invention may be accomplished by those skilled in the art, but I desire to claim all such modifications and combinations as properly come within the scope of my invention.

I claim:

1. An electronictiming and control device comprising:

sensor means for developing an electrical signal indicative of the concentrate density' of a fluid; injection means for adding concentrate to the fluid; and switching means for triggering the-operation of said injection means, said switching means being coupled to said sensor means, meansresponsive tosaid switching means for holding said injection means in an operating state for a predetermined period of time and for turning ofF' said injections means after the lapse of saidpredetermined. period of time, means for delaying a subsequent triggering on of said injections means, and said switching means for triggering the operation of said injection means including a first electronic switching device and capacitance means coupled to said sensor means and being chargeable therefrom and being coupled to the input of said switching device in such a manner as to provide the input triggering signal therefor. 2. An electronic timing and control device in accordance with claim 1 wherein said means for holding said injection means in an operating state comprises:

second and third electronic switching devices, said second electronic switching device being coupled to said first electronic switching device in such a manner as to cause said first device to conduct only when said second device conducts, said third electronic switching device being coupled to said second device in a manner to be turned on by the conduction of said second device; and

means responsive to the conduction of said third electronic switching-device for altering the bias conditions of said second switching device.

3. An electronic timing and control device in accordance with claim 2 wherein said means for altering the bias conditions of said second switching device includes feedback means from said third switching device to said second switching device for reducing the forward bias required at said first switching device to cause conduction of said first and second and hence said third switching devices.

4. A electronic timing and control device in accordance with claim 1 wherein said means for delaying a subsequent triggering on of said injection means comprises a capacitor having one terminal thereof coupled both to the output of said sensor means and to the input of said switching means, means for discharging said capacitor during the turn on" time of said injections means, and means biasing said switching means for turning on" the same at a given charge level of said capacitor.

5. The combination comprising: means for sensing the concentrate density of a fluid, indicator means for developing a signal indicative of the sensed concentration;

first, second, and third switching means; said first switching means coupled to said. indicator means, said first and second switching means being coupled together such that the turn on conditions of both said first and second switching means must be satisfied prior to the conduction of either of said first and second switching means;

means affecting the bias of said second switching means during the conduction thereof in sucha manner as to cause the turn off conditions of said first switching means to be substantially less than the turned on" condi-- tions thereof; and

said second'switching means being coupled to saidthird?" switching means so as to turn on" the same, injection:

means responsive to the operating state of said third switching means for adding concentrate to said fluid.

6. The combination in accordance with claim 5 wherein said means affecting the bias of said second switching means is coupled to and is responsive to the operating state of said third switching means.

7. The combination in accordance with claim 5 wherein a capacitor is coupled to the output of said indicator means and to the input of said first switching means, wherein said indicator means charges said capacitor, agiven charge on said capacitor causing the conduction of said first switching means, and wherein the turning on" of said first, second and third switching means provides a discharge path for said capacitor, thereby ceasing the conduction of said switching means.

8. The combination in accordance with claim 5 wherein said 

